The present invention relates generally to radar mapping systems and to navigation positioning systems, and more specifically to a map-matching radar navigation system.
Many United States military aircraft and ships rely on the Global Positioning System (GPS) as a navigation system that provides a world wide navigation network through the use of a ring of satellites. Examples of GPS navigational systems are disclosed in the following references, which are incorporated herein by references:
U.S. Pat. No. 3,461,421 issued to H. Stover on 12 Aug. 1968;
U.S. patent application Ser. No. 666,784 filed on 31 Oct. 1984 by Edwin Westerfield; and
U.S. patent application Ser. No. 377,214 filed on 11 May 1982 by Richard Lane.
The Stover reference discloses a sonobuoy system which has direction finding and range capabilities. The Westerfield and Lane references described the use of a Global Positioning System to determine the geodetic location of a single sonobuoy in an array of sonobuoys and, in turn the determination of the splash point re-entry vehicles.
While the GPS navigation system is admirable in may respects, it is subject to jamming by electromagnetic interference. For this reason, there exists the need for an independent navigation system that is capable of providing accurate position updates to airborne platforms. In use, this independent system can serve as a backup to existing navigational systems, or in the alternative is capable of acting as the primary navigation system for aircraft.
The task of providing an airborne radar map-matching navigation system is alleviated to some extent, by the system disclosed in the following U.S. Patents, the disclosures of which are incorporated by reference:
U.S. Pat. No. 2,705,319 issued to Dauber;
U.S. Pat. No. 3,054,999 issued to Forbath et al;
U.S. Pat. No. 3,605,556 issued to Kaufman;
U.S. Pat. No. 4,106,726 issued to Emmons et al;
U.S. Pat. No. 4,277,137 issued to Upatnieks et al;
U.S. Pat. No. 3,076,961 issued to Bibbero;
U.S. Pat. No. 3,701,158 issued to Johnson;
U.S. Pat. No. 4,122,421 issued to Rick et al;
U.S. Pat. No. 4,160,251 issued to Lazarchik et al; and
U.S. Pat. No. 4,447,814 issued to Brumbaugh et al
Dauber discloses an airborne system for the detection of changes in terrain reflection coefficient. The patented system uses changes in the reflection of radio waves to detect and fix the location of camouflaged military installations.
Emmons et al discuss a prestored area correlation tracker which relies on multiple digital representations of a target scene. Suitable optical sensors associated with the patented tracker serve to detect changes in tracker spatial orientation, which in turn are used by a missile autopilot to properly steer the missile to the target.
A correlation evaluator for a map matching navigation system is disclosed in Forbath et al. Upatnieks et al are concerned with a terminal guidance system using coherent optical correlation. Kaufman discloses a system for homing a missile on target which distinguishes a change in light intensity in the area immediately surrounding the target.
Lazarchil et al disclose a radiometric system for target recognition which operates in both active and passive modes. In column 3, beginning line 36, this patent states "In the active mode of the hybrid radiometer, the return signal measurement is based upon the backscattering properties of the terrain." The patented system is described as providing discrimination against jamming and spurious signals. Bibbero shows a coordinated three-mode system for aerial reconnaissance which combines infrared, TV and radar coverages. Johnson provides a directional antenna for sensing both radio waves reflected from a target and infrared rays emanating from the target. A dual mode radio frequency-infrared frequency energy seeker system is disclosed in Brumbaugh et al.
Rick et al relate to a multiple sensor system for airborne reconnaissance. The sensors of this patent may be cameras, magnetic recording devices, radar sets, or other type of detector capable of simultaneous operation in the same system.
While the above-cited references are instructive, a need remains to provide an airborne radar map-matching navigation system. The present invention is intended to satisfy that need.